A cellular network is a wireless communications system made up of a number of cells, each served by a fixed transmitter, known as a cell site or base station. Each cell site in the network typically overlaps other cell sites. The most common form of cellular network is a mobile phone (cell phone) system. The base stations are connected to cellular telephone exchanges or “switches”, which in turn connect to the public telephone network or another switch of the cellular company.
The 3rd Generation Partnership Project (3GPP) is a worldwide consortium to create a specification for a globally applicable third generation (3G) mobile phone system. 3GPP's plans are currently in development under the title Long Term Evolution (LTE). The 3GPP LTE project is to improve the Universal Mobile Telecommunications System (UMTS) terrestrial radio access mobile phone standard to cope with future requirements. Goals of 3GPP LTE include improving efficiency, lowering costs, improving services, making use of new spectrum opportunities, and better integration with other open standards. The 3GPP LTE technical specification is described in a set of reference documents including 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Physical Channels and Modulation (Release 8), 3GPP TS 36.211 V0.4.0 (2007-02); and 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 (Release 8), 3GPP TS 36.300 V8.1.0 (2007-06). In 3GPP LTE (E-UTRA and E-UTRAN) terminology, a base station is called an “eNode-B” (eNB) and a mobile terminal or device is called a “user equipment” (UE).
Mobile devices (UEs) require battery power to operate. One of the goals of E-UTRA and E-UTRAN is to provide power-saving possibilities for the UEs. Discontinuous reception (DRX) is a method used in mobile communications to conserve the battery of the mobile device. The mobile device and the network negotiate phases in which data transfer happens. During other times the mobile device turns its receiver off and enters a low-power state.
In 3GPP LTE, the mobile devices must be able to transmit and receive voice-over-internet-protocol (VoIP) data packets. The VoIP traffic pattern has periodic small data packets at fixed intervals and periodic silence indication (SID) packets. Also, 3GPP LTE uses a hybrid automatic repeat-request (HARQ) method, a variation of the well-known automatic repeat-request ARQ method, to transmit the VoIP packets. HARQ requires an acknowledgment signal (ACK) or negative-acknowledgement signal (NACK) to be sent by the receiver back to the transmitter to indicate that the VoIP packet has been received or not received. If the transmitter receives a NACK, then the VoIP packet is retransmitted.
The unique VoIP traffic pattern and the requirement for ACK/NACK transmissions and VoIP packet retransmissions present special challenges to the use of DRX to minimize power consumption in a mobile device. The mobile device's receiver must be turned on to receive the periodic VoIP packets and SIDs as well as the ACK/NACK signals and retransmitted VoIP packets. What is needed is a system and method for controlling DRX in a mobile device that allows operation with these requirements, but that also minimizes power consumption.